There have widely been used numerical control systems for controlling a number of axes or spindles with a plurality of channels (functional arrangements). Such numerical control systems include a numerical control system for controlling a four-axis lathe having two spindles and two tool rests. A workpiece can be machined at a high speed by the spindles or tool rests. With the four-axis lathe or the like, controllers each for controlling one of the spindles and one of the tool rests are fixed or switched by parameters.
Numerical control apparatus have been proposed which make up a complex numerical control system with an increased number of channels (functional arrangements) in order to control a complex machine tool.
If spindles or automatic tool changer controllers are controlled in a fixed manner in the numerical control system with a number of channels, then a long period of time is wasted, and it is difficult to achieve efficient machining operation. Therefore, it is desired that the numerical control system be controlled more flexibly.